What is Relative Humidity and How to Measure It
- Nguyen Vinh Loc
- Jul 9, 2024
- 14 min read
Updated: 6 days ago
Knowing how to measure relative humidity (RH) is essential for controlling indoor comfort, protecting stored goods, and ensuring process efficiency in various industries. Relative humidity is the percentage ratio of the actual water vapor in the air to the maximum it can hold at a specific temperature.
You can measure relative humidity using instruments such as hygrometers, digital humidity sensors, or the psychrometric method. Each method varies in accuracy, cost, and ease of use, but all provide valuable insights for climate control and quality assurance.
In this article, we’ll explain what relative humidity is, why it’s important, and the most reliable ways to measure it—so you can make informed decisions for your home, workplace, or industrial facility.
What is Relative Humidity?
Relative humidity (RH) is the percentage of water vapor present in the air compared to the maximum amount the air can hold at a given temperature. When the air reaches 100% RH, it is fully saturated, meaning any additional moisture will condense into water droplets, often appearing as fog or dew.
Unlike absolute humidity, which measures the actual amount of moisture in grams per cubic meter of air, relative humidity is temperature-dependent. Warm air can hold more moisture, so the same amount of water vapor will result in a lower RH at higher temperatures and a higher RH at lower temperatures.
This relationship explains why indoor air often feels drier in winter—even if the absolute amount of moisture is unchanged, colder air has a reduced capacity to hold water vapor, increasing the likelihood of low RH readings.
Monitoring relative humidity is important because it directly affects human comfort, health, and product quality in industries such as manufacturing, agriculture, and storage. Maintaining an optimal RH range—generally 30–60% for indoor environments—helps prevent mold growth, reduce static electricity, and preserve sensitive materials.
Why Measuring Relative Humidity Matters
Monitoring and controlling relative humidity (RH) is not just a technical task—it directly impacts comfort, safety, product quality, and operational efficiency. Because RH changes with temperature, relying on temperature data alone can be misleading. Measuring RH gives you the missing context to make accurate environmental decisions.
Preserving Product Quality
In sectors such as food processing, pharmaceuticals, and electronics manufacturing, humidity measurement plays a decisive role in protecting product integrity from production to storage.
Food Industry – Excess humidity inside packaging facilities or cold storage can trigger condensation, leading to mold growth and faster spoilage. For instance, a dairy processing plant storing cheese at 85% RH instead of the optimal 70–75% can face accelerated microbial activity, drastically shortening shelf life. By measuring relative humidity continuously, operators can activate dehumidifiers before moisture levels reach a danger point.
Pharmaceuticals – Many drugs, especially tablets and capsules, are hygroscopic—they absorb moisture from the air. Even a small deviation from the recommended RH range (often 45–55%) can alter their chemical composition, reduce potency, or cause physical degradation such as clumping. Regulatory bodies like the FDA require strict humidity measurement tools in production lines to ensure product safety and compliance with Good Manufacturing Practices (GMP).
Electronics Manufacturing – Low RH (<30%) increases the risk of electrostatic discharge (ESD), which can silently damage sensitive electronic components. Conversely, excessively high RH can cause corrosion of metal contacts. Installing humidity measuring devices in cleanrooms and assembly lines allows manufacturers to maintain an optimal balance (typically 40–60% RH), protecting product performance and longevity.
Ultimately, measuring humidity is not just a quality control checkbox—it is a preventive safeguard against losses that could run into millions of dollars annually.
Protecting Health and Comfort
In environments where people spend long periods of time—homes, offices, hospitals, and schools—measuring relative humidity is essential for both physical health and overall comfort.
Respiratory Health – When indoor RH falls below 30%, the air becomes excessively dry. This can irritate mucous membranes, aggravate asthma, and increase susceptibility to respiratory infections because viruses like influenza survive longer in dry air. By installing humidity measurement tools, building managers can ensure RH stays in the ideal range of 40–60%, which research shows reduces airborne virus survival rates.
Skin and Eye Comfort – Low humidity accelerates moisture loss from skin and eyes, leading to dryness, itchiness, and discomfort. This is especially common in winter when heating systems lower indoor RH. A simple humidity measuring device in living spaces allows occupants to monitor dryness and operate humidifiers only when necessary, preventing discomfort without over-humidifying.
Allergen Control – On the other hand, high RH above 60% promotes dust mite populations and mold growth, both of which trigger allergies and asthma attacks. Continuous humidity measurement in hospitals and elder care facilities is critical for maintaining a safe environment for sensitive individuals.
Workplace Productivity – Comfort levels directly influence employee focus and productivity. Offices that maintain stable RH within the recommended range can reduce absenteeism caused by respiratory issues and improve occupant well-being—making measuring humidity a low-cost investment with high returns.
Industrial Processes and Equipment Protection
In many manufacturing and processing facilities, measuring relative humidity is not just about comfort—it’s a critical operational parameter that directly impacts production efficiency, equipment lifespan, and product yield.
Paper and Printing Industry – Paper fibers expand and contract based on moisture content. If RH is too low (<35%), paper becomes brittle and prone to cracking during high-speed printing. If RH is too high (>60%), sheets can curl or cause misfeeds in machinery. Installing humidity measurement tools at key production points allows operators to stabilize moisture levels, ensuring consistent print quality and preventing costly downtime.
Textile Manufacturing – In spinning and weaving, fibers such as cotton, wool, and synthetic blends behave differently depending on air moisture. Insufficient RH can cause static buildup, leading to thread breakage, while excessive RH can weaken yarn strength. Humidity measuring devices help maintain optimal RH (often 50–65%) for smoother operations and reduced material waste.
Metalworking and Electronics Assembly – High humidity accelerates corrosion of machinery components, electrical contacts, and precision instruments. In electronics assembly, an unstable RH can also lead to electrostatic discharge (ESD) damage. Measuring humidity continuously enables predictive maintenance—activating dehumidifiers, adjusting HVAC systems, or triggering alarms before humidity reaches harmful thresholds.
Food and Beverage Processing – From brewing to confectionery, moisture levels affect everything from fermentation rates to sugar crystallization. A brewery fermenting beer at an uncontrolled RH may experience unwanted flavor changes or microbial contamination. With humidity measurement integrated into process control systems, operators can ensure consistency across batches and maintain compliance with hygiene standards.
For industries with high-value equipment, monitoring and controlling RH is one of the simplest ways to extend asset life, reduce unplanned maintenance, and maintain consistent production quality.
Agricultural Applications
In agriculture, measuring relative humidity is vital for both crop health and post-harvest preservation. From greenhouses to grain storage, precise humidity control can mean the difference between maximum yield and significant losses.
Greenhouse Cultivation – Plants rely on a balance between air temperature and RH to regulate transpiration. If RH drops too low (<40%), plants lose water rapidly, leading to stress and reduced growth. Conversely, RH above 80% encourages fungal diseases like powdery mildew and botrytis. Installing humidity measuring devices connected to automated ventilation systems allows growers to maintain the optimal RH range for each crop type, improving yield quality and reducing chemical usage.
Grain and Seed Storage – In silos, excessive RH causes grain kernels to absorb moisture, increasing the risk of mold growth, insect infestation, and spoilage. For example, wheat stored above 14% moisture content can become unsuitable for milling. Humidity measurement tools installed in storage facilities help farmers monitor ambient RH and take corrective actions—such as activating aeration fans—to keep products within safe limits.
Livestock Environments – In poultry houses, pig barns, and cattle sheds, high RH combined with warm temperatures can create heat stress and promote bacterial growth. Maintaining RH within a safe range improves animal welfare, reduces respiratory illness, and enhances feed efficiency. Wireless humidity measurement sensors make it easy to track conditions across large or remote facilities in real time.
Post-Harvest Processing – For crops like coffee, cocoa, and tobacco, drying under controlled humidity prevents uneven moisture distribution, which can affect flavor, texture, and market value. Measuring humidity throughout the drying process ensures consistent results and maximizes product quality.
For farmers, continuous RH monitoring is not just a best practice—it’s a profit safeguard, enabling data-driven decisions that directly protect their bottom line.
HVAC and Building Management
In commercial, industrial, and residential buildings, measuring relative humidity is an essential part of maintaining a healthy, efficient, and comfortable indoor environment. For facility managers, accurate RH data is the foundation for optimizing heating, ventilation, and air conditioning (HVAC) performance.
Energy Efficiency – HVAC systems that operate without RH data often overcool or overheat spaces in an attempt to control comfort levels, leading to unnecessary energy consumption. By integrating humidity measuring devices into building automation systems, operators can adjust temperature and ventilation in sync with actual moisture levels—reducing energy bills and minimizing wear on equipment.
Mold and Structural Protection – Excessive RH (>60%) in walls, ceilings, and crawl spaces can lead to mold growth and structural damage. Over time, trapped moisture can compromise insulation, warp wooden frames, and corrode metal components. Continuous humidity measurement provides early warnings, enabling preventative action before costly repairs are needed.
Compliance and Standards – In specialized facilities such as museums, data centers, and laboratories, RH must be kept within strict limits (often ±5% tolerance) to comply with preservation, safety, or operational standards. Wireless humidity sensors offer precise, in-time data that can be logged for audits or regulatory reporting.
Occupant Comfort and Well-Being – RH directly affects how people perceive temperature. An office at 24°C with 50% RH feels comfortable, but the same temperature at 80% RH can feel oppressive. Measuring RH allows building managers to fine-tune climate conditions, improving comfort without excessive heating or cooling.
For building management teams, monitoring and controlling RH is a low-cost strategy that delivers high returns—protecting assets, ensuring occupant satisfaction, and optimizing operational costs.
How to Measure Relative Humidity
Measuring relative humidity (RH) means determining the amount of water vapor in the air compared to the maximum it can hold at a specific temperature. This is expressed as a percentage. Below are the most common methods — with emphasis on solutions where Daviteq provides industrial-grade products.
Digital Hygrometer
An industrial-grade digital hygrometer is a precision tool designed to measure relative humidity with high accuracy in demanding environments such as manufacturing plants, laboratories, warehouses, or cleanrooms. Built with rugged housings and premium sensing elements, these devices can withstand harsh conditions while maintaining calibration over long periods.
Unlike IoT-enabled wireless sensors that transmit data remotely, a digital hygrometer typically provides readings directly on a built-in display, often alongside temperature values. This makes it ideal for on-site inspections where immediate results are needed. In many cases, these instruments can also connect to building management systems (BMS) or standalone data loggers to store readings for compliance, audits, or quality control records.
Industrial hygrometers are commonly used to verify humidity levels during production runs in food or pharmaceutical facilities, to monitor climate-controlled storage protecting paper, textiles, or electronics, and to support quality assurance inspections in regulated industries. They offer the advantage of delivering instant, highly accurate readings and performing reliably in varying environmental conditions.
However, they are generally standalone devices, which means they do not automatically send data over long distances without additional equipment. For large-scale facilities requiring continuous monitoring, manual checking can become time-consuming, making them better suited for targeted spot measurements rather than full-scale networked monitoring.
Psychrometer
A psychrometer is a classic instrument for measuring relative humidity, relying on the principle of comparing two temperature readings: one from a dry-bulb thermometer and another from a wet-bulb thermometer. The dry-bulb measures the ambient air temperature, while the wet-bulb is covered with a water-soaked cloth that cools as water evaporates. The rate of evaporation — and therefore the temperature difference between the two thermometers — depends on the amount of moisture in the air.
By using a psychrometric chart or calculation formula, the relative humidity can be determined from this temperature difference. This method is highly reliable, and for decades it has been a standard reference in meteorology, HVAC testing, and industrial climate control.
Psychrometers come in two main types: sling psychrometers, which are swung through the air by hand to ensure adequate airflow over the thermometers, and stationary psychrometers, which may use a small fan to provide constant airflow. The sling type is simple, durable, and does not require a power source, making it useful for fieldwork. The stationary type offers better stability and is often used indoors or in controlled environments.
Although psychrometers are robust and can provide accurate readings without electronic components, they require manual operation and calculation, which can be time-consuming compared to digital or IoT-enabled solutions. They are best suited for calibration purposes, educational demonstrations, or as a backup when electronic instruments are unavailable.
Humidity Data Loggers
Humidity data loggers are electronic devices designed to measure and record relative humidity (and often temperature) over extended periods. Unlike handheld hygrometers or psychrometers that provide a reading at a single moment, data loggers automatically capture measurements at set intervals — from every few seconds to once a day — and store them in internal memory for later retrieval.
These devices are essential in environments where long-term humidity trends matter, such as museums, archives, pharmaceutical warehouses, greenhouses, and cold storage facilities. By reviewing historical data, operators can identify fluctuations, detect gradual changes, and address potential issues before they cause damage or regulatory non-compliance.
Most modern humidity data loggers come with USB, Bluetooth, or wireless connectivity, allowing stored data to be downloaded to a computer or synced with cloud-based monitoring platforms. Higher-end industrial models may even integrate directly with IoT systems for real-time alerts when humidity levels go outside acceptable ranges.
The key advantages of data loggers include hands-off operation, high storage capacity, and the ability to maintain a reliable record for audits or compliance reports. However, they are typically not intended for instant spot checks — reviewing the data requires downloading or connecting to a monitoring system. For continuous in-time visibility, they are often combined with networked humidity sensors to provide both historical and real-time insights..
Dew Point Meters
A dew point meter measures the temperature at which moisture in the air begins to condense into liquid — known as the dew point temperature. While relative humidity (RH) tells us how saturated the air is with water vapor, the dew point provides a more absolute measure of moisture content in the air. The lower the dew point, the drier the air; the higher the dew point, the more humid it feels.
Dew point meters are critical in industrial processes, particularly where even small amounts of moisture can cause damage, such as in compressed air systems, gas pipelines, pharmaceutical manufacturing, and electronics production. For example, in compressed air applications, excess moisture can lead to corrosion, equipment failure, and contamination of end products — making dew point monitoring essential for quality control.
Modern dew point meters use chilled mirror sensors, capacitive humidity sensors, or polymer-based sensing technology to provide highly accurate measurements. Many devices also display RH and temperature alongside dew point, offering a more complete picture of ambient conditions. Portable models are available for field inspections, while fixed-installation units continuously monitor critical systems and can trigger alarms when moisture levels exceed set limits.
One of the main advantages of dew point meters is their direct link to process safety and product quality. While RH can vary significantly with temperature, dew point remains a stable reference for evaluating moisture risk, especially in controlled industrial environments. This makes them indispensable for preventive maintenance and regulatory compliance in sensitive industries.
IoT-Enabled Wireless Sensors
In industrial, smart agriculture, and building management applications, IoT-enabled wireless humidity sensors are the most efficient solution for accurately measuring Relative Humidity (RH) with high precision, flexible scalability, and minimal maintenance requirements. Instead of manual checks, these devices automatically collect and transmit in-time RH data to a central system, enabling managers to make quick, data-driven decisions.
These sensors operate on capacitive sensing technology, detecting changes in the dielectric constant as humidity levels fluctuate. Combined with low-power wireless transmission (LoRaWAN, Sigfox, or NB-IoT), the data is sent to a gateway or directly to the cloud. From there, it can be accessed through the Daviteq Globiots IoT Platform or integrated into existing SCADA/BMS systems. In addition, the sensors can calculate related parameters such as dew point, temperature compensation, and long-term humidity trends. Compared to traditional instruments, Daviteq’s wireless solutions offer:
Continuous and automated data collection, eliminating gaps in monitoring.
Remote data access via cloud or mobile app, without on-site visits.
High accuracy (±2–3% RH in industrial-grade models).
Easy integration with automation systems.
Up to 10 years of battery life, reducing maintenance costs.
Automated alerts when thresholds are exceeded.
Practical applications include:
Smart agriculture – monitoring greenhouse humidity to prevent fungal diseases and optimize crop yield, working alongside soil moisture sensors for precise irrigation control.
Industrial warehouses – tracking the storage environment for humidity-sensitive goods such as pharmaceuticals, electronics, or timber, and sending alerts when RH exceeds safe limits.
Cold chain logistics – ensuring perishable goods stay within strict temperature and humidity ranges during transportation.
Cleanrooms and laboratories – maintaining compliance with ISO 14644 or GMP standards.
By moving from manual hygrometers to Daviteq’s IoT-enabled wireless sensors, businesses eliminate data blind spots, reduce labor costs, and gain immediate, reliable insights — critical for process optimization and regulatory compliance.
Factors Affecting Relative Humidity Measurement Accuracy
Measuring relative humidity (RH) may seem straightforward, but achieving reliable results requires understanding the factors that can influence sensor performance. Even the most advanced instruments can deliver inaccurate readings if these variables are overlooked.
Temperature Influence
Relative humidity is temperature-dependent — warm air can hold more moisture than cool air. If the temperature around the sensor fluctuates rapidly, or if the sensor is exposed to a heat source (like direct sunlight, machinery, or HVAC vents), readings can be skewed. Industrial-grade sensors, such as Daviteq’s LoRaWAN and Sigfox humidity sensors, incorporate built-in temperature compensation to minimize these errors.
Sensor Placement
Where you install the device matters as much as the device itself. Placing a sensor too close to walls, air vents, or machinery can result in localized microclimates that don’t represent the actual ambient conditions. For optimal accuracy, RH sensors should be installed at representative heights and away from any heat or moisture sources that could bias results.
Calibration & Maintenance
Over time, all humidity sensors experience drift — a gradual loss of accuracy caused by material aging or environmental exposure. Regular calibration ensures that readings remain within the specified accuracy range. Daviteq sensors can be remotely configured and monitored, allowing for proactive maintenance without physical intervention in hard-to-reach locations.
Environmental Interference
Dust, chemical vapors, or condensation can coat the sensor element, slowing its response or producing false readings. In harsh industrial or agricultural environments, sensors should have protective housings (IP67 or higher) and be positioned where contaminants are minimal. This is why Daviteq’s IP67-rated enclosures are designed to withstand dust, rain, and washdowns.
Response Time
Some applications, such as climate-controlled storage or precision agriculture, require sensors that respond quickly to changing conditions. Slow-response sensors may fail to detect short-term fluctuations, potentially compromising product quality or operational control. Low-power yet high-performance sensing elements, like those used in Daviteq devices, balance fast response times with extended battery life of up to 10 years.
By accounting for these factors during planning, installation, and maintenance, you can ensure that your RH measurements are both accurate and actionable — enabling better decision-making across industrial, commercial, and agricultural settings.
Best Practices for Reliable Relative Humidity Monitoring
Even the most advanced humidity sensors can deliver inaccurate data if they are installed or maintained improperly. To ensure reliable measurements that truly reflect environmental conditions, consider the following best practices.
Select the right sensor type
Choose a humidity sensor technology that matches your application needs. Capacitive sensors offer broad RH measurement ranges with good stability, while resistive sensors are cost-effective for moderate precision needs. For distributed or remote monitoring, IoT-enabled wireless sensors—like Daviteq’s LoRaWAN or Sigfox models - provide long battery life and real-time connectivity without extensive wiring.
Ensure proper installation
Sensor placement can make or break data accuracy. Mount devices in locations that reflect the area’s true conditions, avoiding direct sunlight, heat sources, vents, or moisture-heavy zones like steam outlets. For large spaces, consider multiple sensors to capture variability.
Follow a calibration schedule
All sensors drift over time. Maintain accuracy by calibrating according to the manufacturer’s recommendations—often annually for industrial applications. Use traceable calibration standards to ensure compliance in regulated industries.
Use protective enclosures
In dusty, wet, or chemically aggressive environments, select sensors with protective housings such as IP67-rated enclosures. This prevents contamination, corrosion, and condensation from damaging the sensing element.
Integrate with data systems
Pair humidity sensors with data acquisition platforms or cloud-based monitoring systems. This not only provides in-time alerts for threshold breaches but also stores historical trends for process optimization and compliance audits.
Train personnel
Ensure that staff understand how to operate, interpret, and maintain the sensors. Well-trained teams can spot anomalies faster and respond before minor deviations become major problems.
By implementing these practices, facilities can move beyond simple monitoring to predictive environmental control—minimizing risks, protecting assets, and meeting quality or regulatory requirements.
Measuring relative humidity isn’t just a technical task—it’s a critical step in safeguarding product quality, ensuring process efficiency, and creating healthier environments. Whether in a greenhouse, a pharmaceutical cleanroom, or an industrial manufacturing line, accurate RH monitoring enables better decision-making and reduces costly risks.
With modern tools like IoT-enabled wireless sensors, data loggers, and industrial-grade hygrometers, businesses can go beyond basic readings to achieve continuous, precise, and actionable humidity control. The key is selecting the right instrument for your application and maintaining it properly to ensure accuracy over time.
At Daviteq, we combine robust sensor design with advanced IoT connectivity, giving you in-time data you can trust—even in the most demanding environments. If you’re ready to optimize your humidity monitoring strategy, now is the perfect time to explore solutions tailored to your industry needs.
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